228 PHYSIOLOGY CHAP. 



partial tones are the octave, the fifth, fourth, major third, minor 

 third, major second, etc. They become smaller as the overtones 

 are higher and as the successive partial tones become weaker 

 and weaker it is obvious that even a trained musical ear will fail 

 to distinguish all the partials contained in a tone. The ear 

 perceives the compound tone as a uniform whole, although it is 

 easy to distinguish the timbre of the different instruments, because 

 in each the number and relative intensity of its partial tones 

 vary, and thus result in a qualitative difference in the sounding 

 mass as a whole. 



In order clearly to distinguish and determine all the partial 

 tones contained in a compound tone, in other words to analyse 

 its different elementary components, it is advisable to employ 

 Helmholtz' resonators. Each resonator is tuned to a definite note 

 of the scale, and is able to reinforce it. Even though it con- 

 tains a number of tones proper to itself it resounds with special 

 intensity to the lowest of them when a sound containing this 

 note is struck near it. By applying each resonator to the ear in 



P^2 * ? 



[Fie. 90. Musical representation of the series of harmonic overtones of the note C=132 <l.v. 



turn, the partials of which a compound tone consists can be 

 strengthened, and become easy to recognise. 



Helmholtz' resonators are hollow metal spheres of different diameter with 

 two openings : from one, the larger, a cylindrical prolongation from the walls 

 of the sphere projects a certain distance, and serves to collect the air- waves 

 coming from the sounding instrument and transmit them to the mass of air 

 confined within the walls of the resonator. The second, smaller, opening is 

 diametrically opposite, and a conical lengthening of the walls of the sphere 

 projects a certain distance from it to make connection with the ear of the 

 observer. 



The several resonators strengthen and make clearer the partial tones from 

 which the compound tone results, in proportion with the mass of air contained 

 in each resonator. The tones heard from each resonator must therefore vary 

 with its size, and in order to analyse the different tones a complete series of 

 resonators, corresponding to the semitones of the scale, must be provided. 



Edelmann reduced the number of resonators to five, with diameters of 

 350, 150, 80, 45, and 30 mm. ; he used the same resonator for analysis of 

 several semitones by placing a series of diaphragms of different diameter 

 upon the receiver. He also improved Helmholtz' resonators by other modi- 

 fications. 



Fig. 91 shows the series of Edelmann's resonators with various diaphragms 

 (a, &, c, d, e) and the rubber tube r, one end of which is to be attached to the 

 resonator, and the other to the observer's ear. 



Fig. 92 shows one of these resonators in section. In this a, 6, c indicates 

 the section of the walls of the hollow sphere, 1 mm. thick. It is interrupted 





